In the field of well drilling, top head drive drilling rigs have gained immense popularity in recent years. These drilling rigs include a tower pivotally mounted on a truck bed, together with a hydraulic pump, an air compressor, and other ancillary equipment. The hydraulic pump actuates leveling jacks, hydraulic pistons to raise the tower, and a hydraulic motor in the top head drive which translates vertically along the tower. The top head drive unit is driven vertically upwardly or downwardly to urge the drill bit into engagement in the hole or to remove the drilling pipe and bit from the hole. In general, top head drive drilling rigs are highly portable, rugged, versatile, and efficient.
Generally speaking, top head drive drilling rigs employ drilling pipe which is provided with threaded couplings at either end. The drilling pipe is generally narrow in outside diameter, and the flow path through the interior of the pipe is restricted by the narrow internal diameter at the tapered, threaded ends thereof. As a result, reverse circulation drilling methods (in which air, water, drilling debris, and the like are pumped out of the well through the interior of the drilling pipe) are not possible with top head drive drilling rigs. Rather, air, water, mud, and the like are injected into the well through the interior of the connected drilling pipes, and the outflow of these materials in the annular space between the drilling pipe and the well circumference carries the drilling debris to the surface. This arrangement is quite effective for drilling shallow or narrow diameter wells.
However, the constrictions caused by the narrow internal diameter at the threaded ends of the drilling pipe prevent the pumping of large volumes of water or mud through the interior of the drilling pipe to any greater depth. As a result, it is difficult to drill large diameter holes with a top head drilling rig, and it is also difficult to pump water or drilling mud to any great depth through the assembled drilling pipes. As a result, deep wells are beyond the reach of top head drilling rigs known in the prior art.